Aircraft powerplants typically need to consume ambient air for the oxygen to react with the hydrogen fuel. At high altitude, air is very low in pressure and density, and must typically be compressed in order to be usable in a powerplant. The power required for this compression can be a significant fraction of the gross output power of the powerplant, so it is important to minimize the power needed for compression so as to minimize the impact on overall system efficiency.
Air pressurization for internal combustion engines is most efficiently accomplished using one or more turbochargers. A turbocharger is a combination of turbine driven by engine exhaust gases and an inlet air compressor driven by the turbine.
In the case where the powerplant is based on a hydrogen internal combustion engine, the air-to-hydrogen mass flow ratio is typically about 70:1. The engine torque is approximately proportional to the amount of hydrogen burned per engine revolution. The amount of air taken in by the engine is proportional to the density of the air fed to the intake manifold. Thus, achieving a desired torque level requires achieving a certain intake air density.
Air density is proportional to pressure divided by temperature. The requisite density can be achieved by any of suitable combination of pressure and temperature. A higher temperature means higher pressure is needed to achieve a desired density, thus, it is known to use an intercooler (e.g., a heat exchanger after the first of two compressors) to cool air after a first compression, and an aftercooler (e.g., a heat exchanger after the second compressor) to cool it again after a second compression.
The more effective at cooling these coolers are, the less energy is expended in compressing the air. However, extensive air cooling devices may cause a pressure drop, counteracting the benefits of the compressor. Thus, it is desirable to maximize the cooling capability of a cooler while minimizing its pressure drop. Typically, the temperature of the coolant used to cool an intercooler or an aftercooler is limited to the ambient temperature of the surrounding air.
Accordingly, there has existed a need for an aircraft powerplant that can provide highly efficient cooling to compressed air, and to other devices needing efficient cooling. Preferred embodiments of the present invention satisfy these and other needs, and provide further related advantages.